One trustworthy memorial of this native civilisation is the famous Calendar Stone: a huge circular block of dark porphyry, disinterred in 1790 in the great square of Mexico, which discloses evidence of progress in astronomical science altogether wonderful in a people among whom civilisation was in other respects so partially developed. The Mexicans had a solar year of 365 days divided into eighteen months of twenty days each, with the five complementary days added to the last. The discrepancy between the actual time of the sun’s annual path through the heavens and their imperfect year, was regulated by the intercalation of thirteen days at the end of every fifty-second year. According to Gama, who differs from Humboldt on this point, the civil day was divided into sixteen parts; and he conceives the Calendar to have been constructed as a vertical sundial. Mexican drawings also indicate that the Aztecs were acquainted with the cause of eclipses. But beyond this our means of ascertaining the extent of their astronomical knowledge fail; while there is proof that their inquiries were zealously directed to the more favoured speculations of the astrologer, which have supplanted true science in all primitive stages of society. Mr. Stephens drew attention to [Illustration: FIG. 74.—Mask, Mexican Calendar Stone.] points of correspondence between the central device on the Calendar Stone, and a mask, with widely expanded eyes and tongue hanging out, prominent in the curious sacrificial scene sculptured on the Casa de Piedra at Palenque. But the correspondence amounts to little more than this, that each is a gigantic mask with protruding tongue. That of the Calendar Stone is engraved here from a cast brought home by Mr. Bullock, and now in the Collection of the Society of Antiquaries of Scotland. The statues dug up along with it on the site of the great teocalli of Mexico, were buried in the court of the University, to place them beyond reach of the idolatrous rites which the Indians were inclined to pay to them. At the solicitation of Mr. Bullock they were again disinterred, to admit of his obtaining casts; and he furnishes this interesting account of the sensation excited by the restoration to light of the largest and most celebrated of the Mexican deities:—“During the time it was exposed, the court of the University was crowded with people, most of whom expressed the most decided anger and contempt. Not so, however, all the Indians. I attentively marked their countenances. Not a smile escaped them, or even a word. All was silence and attention. In reply to a joke of one of the students, an old Indian remarked, ‘It is very true we have three very good Spanish gods, but we might still have been allowed to keep a few of those of our ancestors!’ And I was informed that chaplets of flowers had been placed on the figure by natives who had stolen thither unseen in the evening.”[95] [Illustration: FIG. 75.—Ticul Hieroglyphic Vase.]